In general, a spirometry test measures the air entering and leaving the lungs and airways and is often used as a preliminary test for assessing the health condition of a patient's lungs and airways as well as a means for periodically tracking the progress of disease treatment and effect of medication. The spirometry test typically is performed using a device known as a spirometer, and the data provided by the test often is provided graphically in the form of a “volume-time curve” in which volume in liters is shown along the Y-axis and time in seconds is shown along the X-axis and/or in the form of a “flow-volume loop” in which the rate of airflow is shown on the Y-axis and the total volume inspired or expired is shown on the X-axis.
By way of example, a few common parameters that may be measured during respiratory testing include: Forced Vital Capacity (FVC) which is the total volume of air that can be forcibly blown out after full inspiration; Forced Expiratory Volume (FEV) at timed intervals (for instance, at 1.0 second (FEV1)); Forced Expiratory Flow (FEF) which is the average flow (speed) of air coming out of the lungs and airways during a specified period of the expiration; and Peak Expiratory Flow (PEF) which is the maximum flow (speed) of air during maximum expiration initiated after full inspiration. These parameters often are provided in raw data form (i.e., in liters, liters/second, liters/minute, etc.) and as a percentage of a predicted value (i.e., a percent of a predicted value for a patient of similar age, height, weight, gender and ethnicity).
Each test typically is repeated three times to ensure reproducibility. The obtained results of the tests are highly dependent on patient cooperation and effort. For meaningful and valid test results to be obtained, the patient must provide vigorous and maximum respiratory effort for full expiration and/or inhalation. Typically, if the test is given during an office visit or at a hospital or the like, the patient will be coached and motivated by the attending nurse, physician, or technician to keep exhaling as hard as possible for a predetermined period of time (i.e. “keep going, don't stop”). However, no such assistance is typically provided during home use of a spirometer. Hence, the obtained home test results may not necessarily be valid if maximal effort is not provided throughout the duration of full expiration or inhalation.